The present invention relates generally to mechanical interface devices between humans and computers, and more particularly to mechanical devices for tracking manual manipulations and providing simulated force feedback.
Virtual reality computer systems provide users with the illusion that they are part of a "virtual" environment. A virtual reality system will typically include a computer processor, such as a personal computer or workstation, specialized virtual reality software, and virtual reality I/O devices such as display screens, head mounted displays, sensor gloves, etc. As virtual reality systems become more powerful and as the number of potential applications increases, there is a growing need for specific human/computer interface devices which allow users to interface with computer simulations with tools that realistically emulate the activities being represented within the virtual simulation.
One common use for virtual reality computer systems is for training. In many fields, such as aviation and vehicle and systems operation, virtual reality systems have been used successfully to allow a user to learn from and experience a realistic "virtual" environment. The appeal of using virtual reality computer systems for training relates, in part, to the ability of such systems to allow trainees the luxury of confidently operating in a highly realistic environment and making mistakes without "real world" consequences. One highly applicable field for the use of virtual training system is medical operations and procedures. A virtual reality computer system can allow a doctor-trainee or other human operator or user to "manipulate" a needle, scalpel or probe within a computer-simulated "body", and thereby perform medical procedures on a virtual patient. In this instance, the I/O device which is typically a 3D pointer, stylus, or the like is used to represent a surgical instrument such as a probe or scalpel. As the "probe" or "scalpel" moves within a provided space or structure, results of such movement are updated and displayed in a body image displayed on a screen of the computer system so that the operator can gain the experience of performing such a procedure without practicing on an actual human being or a cadaver.
Other uses for virtual reality computer systems include entertainment. Sophisticated simulations and video games allow a user to experience virtual environments with high degrees of realism, thus providing highly interactive and immersive experiences for the user.
For virtual reality systems to provide a realistic (and therefore effective) experience for the user, sensory feedback and manual interaction should be as natural and complete as possible. One essential sensory component for many experiences is the "haptic" and tactile senses. The haptic sense is typically related to the sense of touch not associated with tactility, such as the forces sensed when pushing or pulling on an object. The tactile sense is more concerned with the texture and feel of a surface or object.
Medical operations and procedures using such medical instruments as catheters, laparoscopes, and needles have a distinct haptic component that is essential to performing the procedures correctly and effectively. For example, epidural anesthesia is a highly delicate procedure performed by anesthesiologists in operations. In this procedure, a four inch needle is directed between two vertebrae in the lower back of the patient, through extremely dense tissue, and into an epidural space no larger than 1/20th of an inch. Overshooting the epidural space may result in a "wet tap" puncturing the dura mater, resulting in severe spinal headaches for the patient, or, in extreme cases, damage to the spinal cord.
This insertion is accomplished only through the sense of feel, i.e., the haptic sense. The vast majority of physicians use a technique known as the "loss of resistance" method. The fluid in the syringe (typically a saline solution or simply air) is retarded by the dense ligaments as the needle is inserted. The administrator will feel a slight "pop" as the ligamentum flavum (the layer positioned just before the epidural space) is punctured, due to a slight pressure drop from entering the epidural space. The contents of the syringe then flow freely into the epidural space, gently expanding the separation of the two tissue layers. A catheter can subsequently be fed through the center of the epidural needle so that an anesthetic can be metered through an IV.
Currently there is no practical and effective training tool to assist trainees in developing proficiency in the administration of epidural anesthesia and like medical procedures. Mannequins and cadavers often do not meet many of the needs of trainees for such precise manipulations. Thus, a highly accurate virtual reality system would be ideal for this and other types of applications, especially a "high bandwidth" interface system, which is an interface that accurately responds to electronic signals having fast changes and a broad range of frequencies as well as mechanically transmitting such signals accurately to a user.
There are number of devices that are commercially available for interfacing a human with a computer for virtual reality simulations. Some of these devices provide "force feedback" to a user, i.e., the user interface device outputs forces through the use of computer-controlled actuators and sensors to allow the user to experience haptic sensations. However, none of these devices is tailored for such precise operations as epidural anesthesia. For example, in typical multi-degree of freedom apparatuses that include force feedback, there are several disadvantages. Since actuators which supply realistic force feedback tend to be large and heavy, they often provide inertial constraints. There is also the problem of coupled actuators. In a typical force feedback device, a serial chain of links and actuators is implemented to achieve multiple degrees of freedom for a desired object positioned at the end of the chain, i.e., each actuator is coupled to the previous actuator. The user who manipulates the object must carry the inertia of all of the subsequent actuators and links except for the first actuator in the chain, which is grounded. While it is possible to ground all of the actuators in a serial chain by using a complex transmission of cables or belts, the end result is a low stiffness, high friction, high damping transmission which corrupts the bandwidth of the system, providing the user with an unresponsive and inaccurate interface. These types of interfaces also introduce tactile "noise" to the user through friction and compliance in signal transmission and limit the degree of sensitivity conveyed to the user through the actuators of the device.
Other existing devices provide force feedback to a user through the use of a glove or "exoskeleton" which is worn over the user's appendages, such as fingers, arms, or body. However, these systems are not easily applicable to simulation environments such as those needed for medical procedures or simulations of vehicles and the like, since the forces applied to the user are with reference to the body of the user, not to a manipulated instrument or control, and the absolute location of the user's appendages or a manipulated instrument are not easily calculated. Furthermore, these devices tend to be complex mechanisms in which many actuators must be used to provide force feedback to the user.
In addition, existing force feedback devices are typically bulky and require that at least a portion of the force feedback mechanism extend into the workspace of the manipulated medical instrument. For example, in simulated medical procedures, a portion of the mechanism typically extends past the point where the skin surface of the virtual patient is to be simulated and into the workspace of the manipulated instrument. This can cause natural actions during the medical procedure, such as placing one's free hand on the skin surface when inserting a needle, to be strained, awkward, or impossible and thus reduces the realism of the simulation. In addition, the mechanism intrudes into the workspace of the instrument, reducing the workspace of the instrument and the effectiveness and realism of many force feedback simulations and video games. Furthermore, this undesired extension into the workspace often does not allow the force feedback mechanism to be easily housed in a protective casing and concealed from the user.
Furthermore, prior force feedback devices often employ low fidelity actuation transmission systems, such as gear drives. For higher fidelity, cable drive systems may be used. However, these systems require that a drive capstan be wrapped several times with a cable and that the cable be accurately tensioned, resulting in considerable assembly time of the force feedback device. There is also energy loss associated with the cable deflection as the capstan turns.
Therefore, a high fidelity human/computer interface tool which can provide force feedback in a constrained space to a manipulated object remote from the mechanism, and which can provide high bandwidth, accurate forces, is desirable for certain applications.